The concept of the 4 stroke engine The type of fuel injection systems

CHAPTER 2 LITERATURE REVIEW

2.0 The history of automotive engine

The engine is the power generator of the vehicles. The history of automotive engine was first introduced in the early 1880s, but all combustion engines still have three requirements that must be met to do their job of providing power – air, fuel, and ignition. The mixture of air and fuel must be compressed inside the engine in order to make it highly combustible and get the most out of the energy contained in the fuel mixture. Since the mixture is ignited within the engine, automobile power plants are called internal combustion engines. Most can be further classified as reciprocating piston engines, since pistons move up and down within cylinders to provide power. This up-and-down motion is converted into turning motion by the crankshaft.

2.1 The concept of the 4 stroke engine

Intake port and exhaust port are the port of the engine. The intake port will be allows the air fuel mixture into cylinder. Burned gases leave the cylinder through the exhaust port. The air is coming from the intake manifold. Four process of the 4 3 stroke engine is intake process, compression process, power process and exhaust process. At the intake process, the inlet valve is opened while the exhaust valve is closed. The piston is come down from top dead centre to bottom dead centre. The mixture is sucked into the cylinder. At the compression process, the inlet valve and exhaust are closed. The piston is come up from bottom dead centre to top dead centre. The mixture is compressed and spark ignites. At the power stroke process, the inlet valve and exhaust valve are closed. The piston is come down from top dead centre to bottom dead centre. The mixture is burn. At the exhaust process, the inlet valve is closed while the exhaust valve is opened. The piston is come up from bottom dead centre to top dead centre. Burnt gas is pushed out of the cylinder. The figure 2.1 shows the concept of four stroke engine: Intake compression power exhaust Figure 2.1 4

2.2 The type of fuel injection systems

The first method for fuel injection is the direct injection into the cylinders, but unfortunately it suffers from an extraordinarily high back-pressure due to its placement, as well as other severe disadvantages. Because of the close proximity of the injectors to the pistons in the cylinder chamber, fuel must be injected progressively to allow for atomization of the fuel and mix with the air before the spark. The fuel must also be able to enter the cylinder chamber flowing against the rising back pressure. Because of the exposure of the injector tips to the combustion process, carbon build-ups easily clog the injector tips. Lastly, a complete atomization and mixing of a homogeneous air and fuel mixture are almost impossible because of the short time frame. With all of these potential problems, this method of injection is avoided for more efficient systems. Throttle body injection, also known as single- point injection or central fuel injection, has been a favourite of manufacturers because of its simplicity and low cost compared to its major competitor, the multi- point injection systems. This system relies on a single fuel injector downstream of the throttle valve, which reduces the effects of the air flow, or a dual jet fuel injector setup, upstream on each side of the butterfly valves. However, there are several disadvantages to the single-point injection system. In a single-point injection system, the fuel has the tendency to condense fashion, partially taking away control of the system. Similarly to the carburettor, the single-point injection has difficulty distributing the fuel mixture accurately to the different cylinders. Lastly, there must be a hot spot in the throttle body to aid in the atomization of the injected fuel as well as preventing icing during cold conditions. Multi-point fuel injection is the most widely used fuel injection system employed in todays automobiles. This system works by injecting fuel into the intake manifold directly into the cylinder head ports. Implementing this direct injection to the cylinder head ports, the multi-port system avoids the previously mentioned disadvantages of the single-point system. The fuel injector is directed to spray onto the hot inlet valves, preventing condensation of the fuel in the port as well as decreasing the likeliness of the fuel mixture being drawn into an adjacent cylinder due to the effects of back pressure. The only real disadvantage of this system is the extra cost from specialized intake manifolds and extra components such as fuel rails, 5 which are outweighed by the better performance achieved. Garrett W. Balich and Conrad R. Aschenbach, 6 May 2004 The figure 2.2 shows the basic fuel system: Figure 2.2 6

2.3 The basic engine parts